The invention relates to a screen-printing squeegee having an elastic application element and a holding apparatus for the application element, the holding apparatus being divided, as viewed over the width of the application element, into a plurality of holding sections which can move with respect to one another. The invention also relates to an apparatus for screen printing having a screen-printing squeegee according to the invention.
The international laid-open specification WO 2005/035250 A1 has disclosed a screen-printing squeegee having an elastic application element in the form of a plate-shaped squeegee rubber. The plate-shaped squeegee rubber is provided with a holding apparatus, wherein impression cylinders which are also connected to a squeegee carrier act on the holding apparatus. For printing, the elastic application element is pressed by means of the impression cylinders in the direction of a printing screen and a printing table and is then moved by means of a movement of the squeegee carrier, parallel to the printing table, over the latter and/or the printing material. The division of the holding apparatus into a plurality of holding sections which can move with respect to one another is provided for the purpose of achieving a certain flexibility of the screen-printing squeegee. In order to print curved surfaces, the squeegee rubber itself is cut in accordance with the contour of the article to be printed.
The invention is intended to specify an improved screen-printing squeegee and an improved apparatus for screen printing which can be used in a flexible way for printing curved surfaces.
To this end, according to the invention, a screen-printing squeegee having an elastic application element and a holding apparatus for the application element is provided, the holding apparatus being divided, as viewed over the width of the application element, into a plurality of holding sections which can move with respect to one another, in which a leaf-spring element is provided interconnecting the holding sections which can move with respect to one another.
As a result of the provision of the leaf-spring element, the screen-printing squeegee is comparatively flexible in the plane of the application element, that is to say perpendicularly with respect to the provided printing direction, since, in this direction, the leaf spring makes a movement of the individual holding sections with respect to one another possible to a comparatively great extent. In contrast, the screen-printing squeegee is of substantially more rigid configuration in and counter to the printing direction, since the leaf-spring element makes only a very limited movement of the individual holding sections with respect to one another possible in this direction. The screen-printing squeegee is therefore of very rigid configuration in and counter to the printing direction, with the result that a precise print is made possible. As a result, curved surfaces can be printed by way of the screen-printing squeegee according to the invention, the flexible and resilient configuration of the screen-printing squeegee in the plane of the application element, that is to say perpendicularly with respect to the printing direction, making it possible to also adapt to changing curvatures and to ensure a uniform profile of the pressing force of the application element on the printing screen and the article to be printed.
The screen-printing squeegee according to the invention is also suitable for printing three-dimensionally curved surfaces, for example glass panes of bowl-like configuration for motor vehicles. The leaf-spring element is configured and arranged in such a way that a spring travel of the individual holding sections is made possible parallel to the plane of the application element, that is to say perpendicularly with respect to the provided printing direction, and a movement of the holding sections with respect to one another in and counter to the printing direction is largely suppressed. The spring action of the leaf-spring element ensures at the same time that an excessive movement of the holding sections with respect to one another is prevented and a continuous, uniform profile of the lower edge of the squeegee element is always ensured, said lower edge being decisive for the printing operation.
In one development of the invention, the leaf-spring element has a leaf spring which is contiguous, extends at least over the length of the squeegee, and from which fastening flanges extend to the individual holding sections.
By means of a contiguous leaf spring which has only one spring leaf in the embodiment which is shown, firstly the desired spring action parallel to the plane of the application element, that is to say perpendicularly with respect to the printing direction, and secondly the desired stiffening of the squeegee perpendicularly with respect to the plane of the application element, that is to say in and counter to the printing direction, can be achieved. The provision of fastening flanges makes the unproblematic arrangement of the leaf spring on the holding apparatus or the individual holding sections possible. In each case one leaf-spring element with holding flanges is advantageously provided in front of and behind the application element, as viewed in the printing direction. In this way, the leaf-spring elements themselves can be of smaller and lighter configuration, since the spring action and the stiffening of the squeegee are achieved by means of the two leaf-spring elements which are arranged in front of and behind the application element.
In one development of the invention, the leaf spring is formed from sheet-metal material and has a width which is greater than a thickness of the leaf spring, the leaf spring being oriented in such a way that the width dimension is arranged parallel to the printing direction and the thickness dimension is arranged perpendicularly with respect to the printing direction and with respect to the printing table.
An arrangement of this type of the leaf spring achieves a situation where a spring movement is possible substantially only perpendicularly with respect to the printing direction and with respect to the printing table, whereas a movement of the individual holding sections with respect to one another in and counter to the printing direction is largely suppressed.
In one development of the invention, the fastening flanges are configured integrally with the web.
In this way, a structurally simple design is achieved and the leaf-spring element can be mounted and dismantled in its entirety in a simple way.
In one development of the invention, the leaf-spring element is configured as a sheet-metal part and the fastening flanges are bent away starting from the web.
For example, the leaf-spring element can be configured in a simple way from spring steel and can be laser cut out, for example. In this case, the leaf spring consists merely of one spring leaf.
The problem on which the invention is based is also solved by an apparatus for screen printing having a screen-printing squeegee according to the invention, in which apparatus a plurality, in particular each, of the holding sections of the screen-printing squeegee are/is assigned an impression cylinder, the impression cylinders being connected firstly to the holding sections and secondly to a squeegee bar which can be moved in and counter to the printing direction, it being possible to set a pressure which loads the impression cylinders separately for at least some of the impression cylinders.
In this way, a different pressure can be set at the impression cylinders, as viewed over the width of the screen-printing squeegee, and a different contact pressure can be set in this way, as viewed over the width of the squeegee. This is of great importance if, when printing curved surfaces, a sufficient contact pressure is to be ensured even in the curvature regions.
In a screen-printing apparatus according to the invention, the impression cylinders are fastened firstly to in each case one holding section and secondly to a squeegee bar, the impression cylinders being arranged on the squeegee bar and/or on the holding sections such that they can be pivoted in each case about a pivot axis which is arranged substantially parallel to the printing direction.
In this way, the impression cylinders can be set in such a way that a force which is exerted on the application element by the impression cylinders acts substantially always perpendicularly with respect to the surface to be printed. The pivoting of the impression cylinders can take place during a setting operation, and the impression cylinders can be fixed in relation to the pivot axes after the setting operation. As an alternative, it can also be provided that the impression cylinders can also pivot about the pivot axes during the printing operation, for example when the curvature of the article to be printed changes as viewed in the printing direction.
In one development of the invention, a pivot axis is arranged approximately halfway up the squeegee bar.
In this way, a stable and geometrically favourable arrangement can be realized.
In one development of the invention, the pivot axis lies immediately above or in the region of the upper edge of the application element.
In this way, a perpendicular introduction of force, which is uniform and substantially perpendicular with respect to the pressing edge of the application element, is possible from the impression cylinders into the holding sections or the application element.
Further features and advantages of the invention result from the claims and the following description of preferred embodiments of the invention in conjunction with the drawings. Individual features which are shown in the different drawings and are described using the exemplary embodiments can be combined with one another in any desired way, without departing from the scope of the invention.